8 FLORA OF ST. CROIX AND THE VIRGIN ISLANDS. 



partly also on the southern part of all the islands, a dry shrubby vege- 

 tation of a greyish or yellowish aspect, which, from the predominating 

 genus composing its elements, I hav called the Croton vegetation. This 

 peculiar kind of dry shrub also occurs here and there in other parts of 

 the islands, where the soil, through reckless cultivation, has become too 

 exhausted to produce a growth of taller trees, and it cannot be estimated 

 to cover less than one third part of the whole surface of the islands, pre- 

 dominating in some, as Tortola, St. Thomas, and Culebra, less conspicu- 

 ous in others, as St. Jan, Vieques, and St. Croix. 



The ravines as well as the northern and western parts of the islands 

 are often covered with a growth of taller trees, forming a kind of forest, 

 composed of species partly evergreen and partly with deciduous foliage, 

 and which, from one of the most prominent forms, I have called the Erio- 

 dendron vegetation. The area covered by this formation may be taken 

 to be about one fifth of the whole surface, the best wooded islands being 

 St. Jan and Yieques, the least wooded ones St. Thomas and Virgin 

 Gorda. 



The remainder of the surface is either used for pasture or cultivated 

 with sugar-cane or provisions, the former on a large scale in St. Croix 

 and Vieques only, the latter everywhere on the islands where the soil 

 seems proper for the purpose. This last section I term 1 he cultivated 

 region. 



Considering first the Croton vegetation, we find here a number of plants 

 which in various ways have become enabled to resist the deteriorating 

 effects of the dry climate, and to exist on the barren rocky soil always 

 found where the moisture is not sufficient for decomposing the natural 

 rock of the surface. Thus, some of these plants, as the whole of the 

 genus Croton, already mentioned above, have small leaves, which, like 

 the stem, are covered with scales and tomentose hair, containing besides 

 aromatic oil, all which contrivances tend to diminish evaporation as much 

 as possible. The most common species of this remarkable genus are C. 

 flavus, astroiteSj bicolor, and betulinus. Other forms obtain the same 

 object by having very small, partly deciduous leaves and their stipules 

 transformed into prickles, especially the Acacias, such as A. Farnesiana, 

 macracantha, tortuosa^ and sarmentosa. Others, again, are rich in milky 

 juice, as Euphorbia petiolaris, Rauwolfia Lamarclm^ and the naturalized 

 Calotropis procera, or merely in aqueous sap, as the Cactese, the common- 

 est forms of which are Melocactus communis, Cereus floccosus, and several 

 species of Opuntia. Others, such as Bromeliacese, on the contrary, have 



